1. Field of the Invention
This invention pertains to the field of packaging of products in heat shrinkable film, and more particularly to the packaging of meat products in high speed production operations.
2. Background of the Invention
A significant quantity of meat products, and particularly poultry products are packaged in heat shrinkable film which is shrunk around the product prior to shipping to a market. The product, such as poultry, is typically supported in a tray which is also included within the film wrapped enclosure.
There are a number of methods of wrapping the tray and product in automated processes. The more prevalent methods may be referred to as the single sheet over-wrap method, the double sheet sandwich method and the single sheet tubular wrap method and which is also called a pillow pack. In the single sheet over-wrap method, a single rectangular sheet of wrapping film is placed over the product and tray, the film is then wrapped around all four sides, and tucked under the bottom for heat sealing. In the double sheet sandwich method the product is positioned between two continuous sheets of film and the four sides are sealed with heating means after which the film is cut behind the trailing end. In the single sheet tubular wrap method, the product and tray are positioned beneath a wide, continuous film, and the two edges are brought down around and under the package, and are sealed together along the center line of the bottom of the tray to form a tube after which the tube is heat sealed, typically by bar sealers, ahead of and behind the package and separated from the rest of the film. The resultant film package is somewhat larger then the product tray and fits loosely prior to being shrunk.
The typical shallow tray of the type to which the invention pertains is molded of a plastic material, has upwardly and outwardly angled side walls and a peripheral flange or lip.
In the case of the double sheet sandwich and single sheet tubular wrap methods, the sealed edges are typically of the order of 3/8" in width and project laterally outward in the vicinity of the tray flanges or lips. The seal width of approximately 3/8" is useful so as to aid in the protection of the meat product by maintaining a hermetic seal. These edges normally occur at a height approximately equal to or higher than that of the tray flanges. As can be readily appreciated, if these sealed edges were to remain in that position and orientation to the point of consumer presentation at the market, the overall appearance of the package would be less than acceptable.
The more desirable position for the sealed edges after shrinking is one that is relatively unobtrusive. Such a position would be below and inside of the periphery of the tray flange. This would make the finished edge unnoticable so that attention of the customer would remain on the product.
The shrinkable film is responsive to heat from a variety of media, such as radiant heat transfer, heated air streams or heated water. The radiant transfer method tends to be slow and less than optimally efficient in a production operation. The heated water method transfers heat effectively, but may require subsequent drying and other clean up. Therefore, the heated air method is generally preferred as being reasonably quick and efficient for the typical relatively high speed production, e.g. forty or more packages per minute.
In the body of prior art on shrink tunnels, U.S. Pat. No. 3,349,502 to Kiefer teaches an apparatus intended to solve the problem addressed by the present invention, but by a different method. As illustrated by FIGS. 1, 2, 4 and 5 in the Kiefer patent, air nozzles direct the heated air generally at the bottom of the wrapped tray, relying on the tunnel enclosure to trap the heat required to shrink the sides and upper surface of the film. By more specific and sequentially applied directed hot air streams at plural stations combined with thermally insulative, rotating conveyor rollers, the present invention improves on the prior technology and creates a better appearing package in a more efficient production process.
Therefore, an object of the present invention is to create a package of poultry or other product which is wrapped in a heat shrinkable film and sealed hermetically at the edges and in which the sealed edges are finished in a position beneath and within the periphery of the tray flanges.
A further object of the present invention is to create such a package in a high speed production operation.
An additional object of the present invention is to create a finished package in which the film is tight and substantially wrinkle free.
Additional objects and benefits will become apparent as the description details the invention.